diff --git a/Android.bp b/Android.bp
index bd4b40f..d0f97db 100644
--- a/Android.bp
+++ b/Android.bp
@@ -147,6 +147,16 @@
 // Framework guests.
 cc_defaults {
     name: "cc_baremetal_defaults",
+    arch: {
+        arm64: {
+            cflags: [
+                // Prevent the compiler from optimizing code using SVE, as the
+                // baremetal environment might not have configured the hardware.
+                "-Xclang -target-feature",
+                "-Xclang -sve",
+            ],
+        },
+    },
     defaults_visibility: ["//visibility:public"],
 }
 
diff --git a/android/config.go b/android/config.go
index 06d71c0..5132c62 100644
--- a/android/config.go
+++ b/android/config.go
@@ -324,6 +324,9 @@
 	AndroidCommonTarget      Target // the Target for common modules for the Android device
 	AndroidFirstDeviceTarget Target // the first Target for modules for the Android device
 
+	// Flags for Partial Compile, derived from SOONG_PARTIAL_COMPILE.
+	partialCompileFlags partialCompileFlags
+
 	// multilibConflicts for an ArchType is true if there is earlier configured
 	// device architecture with the same multilib value.
 	multilibConflicts map[ArchType]bool
@@ -373,6 +376,16 @@
 	ensureAllowlistIntegrity bool
 }
 
+type partialCompileFlags struct {
+	// Is partial compilation enabled at all?
+	enabled bool
+
+	// Whether to use d8 instead of r8
+	use_d8 bool
+
+	// Add others as needed.
+}
+
 type deviceConfig struct {
 	config *config
 	OncePer
@@ -382,6 +395,88 @@
 	SetDefaultConfig()
 }
 
+// Parse SOONG_PARTIAL_COMPILE.
+//
+// SOONG_PARTIAL_COMPILE determines which features are enabled or disabled in
+// rule generation.  Changing this environment variable causes reanalysis.
+//
+// SOONG_USE_PARTIAL_COMPILE determines whether or not we **use** PARTIAL_COMPILE.
+// Rule generation must support both cases, since changing it does not cause
+// reanalysis.
+//
+// The user-facing documentation shows:
+//
+// - empty or not set: "The current default state"
+// - "true" or "on": enable all stable partial compile features.
+// - "false" or "off": disable partial compile completely.
+//
+// What we actually allow is a comma separated list of tokens, whose first
+// character may be "+" (enable) or "-" (disable).  If neither is present, "+"
+// is assumed.  For example, "on,+use_d8" will enable partial compilation, and
+// additionally set the use_d8 flag (regardless of whether it is opt-in or
+// opt-out).
+//
+// To add a new feature to the list, add the field in the struct
+// `partialCompileFlags` above, and then add the name of the field in the
+// switch statement below.
+func (c *config) parsePartialCompileFlags() (partialCompileFlags, error) {
+	defaultFlags := partialCompileFlags{
+		// Set any opt-out flags here.  Opt-in flags are off by default.
+		enabled: false,
+	}
+	value := c.Getenv("SOONG_PARTIAL_COMPILE")
+
+	if value == "" {
+		return defaultFlags, nil
+	}
+
+	ret := defaultFlags
+	tokens := strings.Split(strings.ToLower(value), ",")
+	makeVal := func(state string, defaultValue bool) bool {
+		switch state {
+		case "":
+			return defaultValue
+		case "-":
+			return false
+		case "+":
+			return true
+		}
+		return false
+	}
+	for _, tok := range tokens {
+		var state string
+		if len(tok) == 0 {
+			continue
+		}
+		switch tok[0:1] {
+		case "":
+			// Ignore empty tokens.
+			continue
+		case "-", "+":
+			state = tok[0:1]
+			tok = tok[1:]
+		default:
+			// Treat `feature` as `+feature`.
+			state = "+"
+		}
+		switch tok {
+		case "true":
+			ret = defaultFlags
+			ret.enabled = true
+		case "false":
+			// Set everything to false.
+			ret = partialCompileFlags{}
+		case "enabled":
+			ret.enabled = makeVal(state, defaultFlags.enabled)
+		case "use_d8":
+			ret.use_d8 = makeVal(state, defaultFlags.use_d8)
+		default:
+			return partialCompileFlags{}, fmt.Errorf("Unknown SOONG_PARTIAL_COMPILE value: %v", value)
+		}
+	}
+	return ret, nil
+}
+
 func loadConfig(config *config) error {
 	return loadFromConfigFile(&config.productVariables, absolutePath(config.ProductVariablesFileName))
 }
@@ -568,6 +663,11 @@
 		return Config{}, err
 	}
 
+	config.partialCompileFlags, err = config.parsePartialCompileFlags()
+	if err != nil {
+		return Config{}, err
+	}
+
 	// Make the CommonOS OsType available for all products.
 	targets[CommonOS] = []Target{commonTargetMap[CommonOS.Name]}
 
@@ -999,6 +1099,10 @@
 	return ApiLevelOrPanic(ctx, codename)
 }
 
+func (c *config) PartialCompileFlags() partialCompileFlags {
+	return c.partialCompileFlags
+}
+
 func (c *config) AppsDefaultVersionName() string {
 	return String(c.productVariables.AppsDefaultVersionName)
 }
diff --git a/android/filegroup.go b/android/filegroup.go
index ff0f74e..a8b4f00 100644
--- a/android/filegroup.go
+++ b/android/filegroup.go
@@ -139,3 +139,15 @@
 
 	return module
 }
+
+// Collect information for opening IDE project files in java/jdeps.go.
+// Copied from build/soong/genrule/genrule.go
+func (fg *fileGroup) IDEInfo(ctx BaseModuleContext, dpInfo *IdeInfo) {
+	dpInfo.Srcs = append(dpInfo.Srcs, fg.Srcs().Strings()...)
+	for _, src := range fg.properties.Srcs.GetOrDefault(ctx, nil) {
+		if mod, _ := SrcIsModuleWithTag(src); mod != "" {
+			// Register the module name without any tags in `Deps`
+			dpInfo.Deps = append(dpInfo.Deps, mod)
+		}
+	}
+}
diff --git a/android/neverallow.go b/android/neverallow.go
index 439fe2d..57373d5 100644
--- a/android/neverallow.go
+++ b/android/neverallow.go
@@ -62,6 +62,7 @@
 	AddNeverAllowRules(createLimitNdkExportRule()...)
 	AddNeverAllowRules(createLimitDirgroupRule()...)
 	AddNeverAllowRules(createFilesystemIsAutoGeneratedRule())
+	AddNeverAllowRules(createKotlinPluginRule()...)
 }
 
 // Add a NeverAllow rule to the set of rules to apply.
@@ -302,6 +303,22 @@
 		Because("is_auto_generated property is only allowed for filesystem modules in build/soong/fsgen directory")
 }
 
+func createKotlinPluginRule() []Rule {
+	kotlinPluginProjectsAllowedList := []string{
+		// TODO: Migrate compose plugin to the bundled compiler plugin
+		// Actual path prebuilts/sdk/current/androidx/m2repository/androidx/compose/compiler/compiler-hosted
+		"prebuilts/sdk/current/androidx",
+		"external/kotlinc",
+	}
+
+	return []Rule{
+		NeverAllow().
+			NotIn(kotlinPluginProjectsAllowedList...).
+			ModuleType("kotlin_plugin").
+			Because("kotlin_plugin can only be used in allowed projects"),
+	}
+}
+
 func neverallowMutator(ctx BottomUpMutatorContext) {
 	m, ok := ctx.Module().(Module)
 	if !ok {
diff --git a/cc/cc_preprocess_no_configuration.go b/cc/cc_preprocess_no_configuration.go
index 3d1d0a5..3d4b077 100644
--- a/cc/cc_preprocess_no_configuration.go
+++ b/cc/cc_preprocess_no_configuration.go
@@ -16,6 +16,7 @@
 
 import (
 	"android/soong/android"
+	"slices"
 	"strings"
 )
 
@@ -78,6 +79,12 @@
 		return
 	}
 
+	cflags := slices.Clone(m.properties.Cflags)
+
+	// Match behavior of other cc modules:
+	// https://cs.android.com/android/platform/superproject/main/+/main:build/soong/cc/compiler.go;l=422;drc=7297f05ee8cda422ccb32c4af4d9d715d6bac10e
+	cflags = append(cflags, "-I"+ctx.ModuleDir())
+
 	var ccCmd string
 	switch src.Ext() {
 	case ".c":
@@ -99,7 +106,7 @@
 		Output:      outFile,
 		Input:       src,
 		Args: map[string]string{
-			"cFlags": strings.Join(m.properties.Cflags, " "),
+			"cFlags": strings.Join(cflags, " "),
 			"ccCmd":  ccCmd,
 		},
 	})
diff --git a/cc/cc_preprocess_no_configuration_test.go b/cc/cc_preprocess_no_configuration_test.go
index 43e726d..c6eae4c 100644
--- a/cc/cc_preprocess_no_configuration_test.go
+++ b/cc/cc_preprocess_no_configuration_test.go
@@ -20,21 +20,24 @@
 )
 
 func TestCcPreprocessNoConfiguration(t *testing.T) {
+	bp := `
+	cc_preprocess_no_configuration {
+		name: "foo",
+		srcs: ["main.cc"],
+		cflags: ["-E", "-DANDROID"],
+	}
+	`
+
 	fixture := android.GroupFixturePreparers(
 		android.PrepareForIntegrationTestWithAndroid,
 		android.FixtureRegisterWithContext(RegisterCCPreprocessNoConfiguration),
+		android.FixtureAddTextFile("foo/bar/Android.bp", bp),
 	)
 
-	result := fixture.RunTestWithBp(t, `
-cc_preprocess_no_configuration {
-	name: "foo",
-	srcs: ["main.cc"],
-	cflags: ["-E", "-DANDROID"],
-}
-`)
+	result := fixture.RunTest(t)
 
 	foo := result.ModuleForTests("foo", "")
 	actual := foo.Rule("cc").Args["cFlags"]
-	expected := "-E -DANDROID"
+	expected := "-E -DANDROID -Ifoo/bar"
 	android.AssertStringEquals(t, "cflags should be correct", expected, actual)
 }
diff --git a/cc/fuzz.go b/cc/fuzz.go
index 0aa9d4b..2b91c57 100644
--- a/cc/fuzz.go
+++ b/cc/fuzz.go
@@ -182,9 +182,13 @@
 }
 
 func (fuzz *fuzzBinary) linkerFlags(ctx ModuleContext, flags Flags) Flags {
-	subdir := "lib"
-	if ctx.inVendor() {
+	var subdir string
+	if ctx.isForPlatform() {
+		subdir = "lib"
+	} else if ctx.inVendor() {
 		subdir = "lib/vendor"
+	} else {
+		ctx.ModuleErrorf("Fuzzer must be system or vendor variant")
 	}
 
 	flags = fuzz.binaryDecorator.linkerFlags(ctx, flags)
diff --git a/filesystem/filesystem.go b/filesystem/filesystem.go
index 4bdd0a4..9756b82 100644
--- a/filesystem/filesystem.go
+++ b/filesystem/filesystem.go
@@ -264,7 +264,7 @@
 func (f *filesystem) filterInstallablePackagingSpec(ps android.PackagingSpec) bool {
 	// Filesystem module respects the installation semantic. A PackagingSpec from a module with
 	// IsSkipInstall() is skipped.
-	return !ps.SkipInstall()
+	return !ps.SkipInstall() && (ps.Partition() == f.PartitionType())
 }
 
 var pctx = android.NewPackageContext("android/soong/filesystem")
diff --git a/filesystem/filesystem_test.go b/filesystem/filesystem_test.go
index 057dcaa..1e50836 100644
--- a/filesystem/filesystem_test.go
+++ b/filesystem/filesystem_test.go
@@ -584,3 +584,28 @@
 	android.AssertStringDoesContain(t, "erofs fs type compress hint", buildImageConfig, "erofs_default_compress_hints=compress_hints.txt")
 	android.AssertStringDoesContain(t, "erofs fs type sparse", buildImageConfig, "erofs_sparse_flag=-s")
 }
+
+// If a system_ext/ module depends on system/ module, the dependency should *not*
+// be installed in system_ext/
+func TestDoNotPackageCrossPartitionDependencies(t *testing.T) {
+	result := fixture.RunTestWithBp(t, `
+		android_filesystem {
+			name: "myfilesystem",
+			deps: ["binfoo"],
+			partition_type: "system_ext",
+		}
+
+		cc_binary {
+			name: "binfoo",
+			shared_libs: ["libfoo"],
+			system_ext_specific: true,
+		}
+		cc_library_shared {
+			name: "libfoo", // installed in system/
+		}
+	`)
+
+	partition := result.ModuleForTests("myfilesystem", "android_common")
+	fileList := android.ContentFromFileRuleForTests(t, result.TestContext, partition.Output("fileList"))
+	android.AssertDeepEquals(t, "filesystem with dependencies on different partition", "bin/binfoo\n", fileList)
+}
diff --git a/filesystem/fsverity_metadata.go b/filesystem/fsverity_metadata.go
index d7bb654..199c845 100644
--- a/filesystem/fsverity_metadata.go
+++ b/filesystem/fsverity_metadata.go
@@ -15,6 +15,7 @@
 package filesystem
 
 import (
+	"fmt"
 	"path/filepath"
 	"strings"
 
@@ -121,8 +122,13 @@
 
 	// STEP 2-2: generate BuildManifest.apk (unsigned)
 	aapt2Path := ctx.Config().HostToolPath(ctx, "aapt2")
-	apkPath := rebasedDir.Join(ctx, "etc", "security", "fsverity", "BuildManifest.apk")
-	idsigPath := rebasedDir.Join(ctx, "etc", "security", "fsverity", "BuildManifest.apk.idsig")
+	apkNameSuffix := ""
+	if f.PartitionType() == "system_ext" {
+		//https://source.corp.google.com/h/googleplex-android/platform/build/+/e392d2b486c2d4187b20a72b1c67cc737ecbcca5:core/Makefile;l=3410;drc=ea8f34bc1d6e63656b4ec32f2391e9d54b3ebb6b;bpv=1;bpt=0
+		apkNameSuffix = "SystemExt"
+	}
+	apkPath := rebasedDir.Join(ctx, "etc", "security", "fsverity", fmt.Sprintf("BuildManifest%s.apk", apkNameSuffix))
+	idsigPath := rebasedDir.Join(ctx, "etc", "security", "fsverity", fmt.Sprintf("BuildManifest%s.apk.idsig", apkNameSuffix))
 	manifestTemplatePath := android.PathForSource(ctx, "system/security/fsverity/AndroidManifest.xml")
 	libs := android.PathsForModuleSrc(ctx, f.properties.Fsverity.Libs)
 	cmd.Implicit(aapt2Path)
diff --git a/filesystem/system_image.go b/filesystem/system_image.go
index 57239ae..7dbf986 100644
--- a/filesystem/system_image.go
+++ b/filesystem/system_image.go
@@ -103,6 +103,6 @@
 // partition.  Note that "apex" module installs its contents to "apex"(fake partition) as well
 // for symbol lookup by imitating "activated" paths.
 func (s *systemImage) filterPackagingSpec(ps android.PackagingSpec) bool {
-	return s.filesystem.filterInstallablePackagingSpec(ps) &&
+	return !ps.SkipInstall() &&
 		(ps.Partition() == "system" || ps.Partition() == "root")
 }
diff --git a/fsgen/filesystem_creator.go b/fsgen/filesystem_creator.go
index f446c2b..dc7becb 100644
--- a/fsgen/filesystem_creator.go
+++ b/fsgen/filesystem_creator.go
@@ -124,10 +124,19 @@
 					"public.libraries.android.txt": defaultDepCandidateProps(ctx.Config()),
 					"update_engine_sideload":       defaultDepCandidateProps(ctx.Config()),
 				},
-				"vendor":     newMultilibDeps(),
-				"odm":        newMultilibDeps(),
-				"product":    newMultilibDeps(),
-				"system_ext": newMultilibDeps(),
+				"vendor":  newMultilibDeps(),
+				"odm":     newMultilibDeps(),
+				"product": newMultilibDeps(),
+				"system_ext": &map[string]*depCandidateProps{
+					// VNDK apexes are automatically included.
+					// This hardcoded list will need to be updated if `PRODUCT_EXTRA_VNDK_VERSIONS` is updated.
+					// https://cs.android.com/android/_/android/platform/build/+/adba533072b00c53ac0f198c550a3cbd7a00e4cd:core/main.mk;l=984;bpv=1;bpt=0;drc=174db7b179592cf07cbfd2adb0119486fda911e7
+					"com.android.vndk.v30": defaultDepCandidateProps(ctx.Config()),
+					"com.android.vndk.v31": defaultDepCandidateProps(ctx.Config()),
+					"com.android.vndk.v32": defaultDepCandidateProps(ctx.Config()),
+					"com.android.vndk.v33": defaultDepCandidateProps(ctx.Config()),
+					"com.android.vndk.v34": defaultDepCandidateProps(ctx.Config()),
+				},
 			},
 			soongGeneratedPartitions: generatedPartitions,
 			fsDepsMutex:              sync.Mutex{},
@@ -226,43 +235,48 @@
 	soongGeneratedPartitionMap := getAllSoongGeneratedPartitionNames(mctx.Config(), fsGenState.soongGeneratedPartitions)
 	m := mctx.Module()
 	if partition, ok := soongGeneratedPartitionMap[m.Name()]; ok {
-		depsStruct := packagingPropsStruct{}
-		for depName, depProps := range *fsDeps[partition] {
-			bitness := getBitness(depProps.Arch)
-			fullyQualifiedDepName := fullyQualifiedModuleName(depName, depProps.Namespace)
-			if android.InList("32", bitness) && android.InList("64", bitness) {
-				// If both 32 and 64 bit variants are enabled for this module
-				switch depProps.Multilib {
-				case string(android.MultilibBoth):
-					depsStruct.Multilib.Both.Deps = append(depsStruct.Multilib.Both.Deps, fullyQualifiedDepName)
-				case string(android.MultilibCommon), string(android.MultilibFirst):
-					depsStruct.Deps = append(depsStruct.Deps, fullyQualifiedDepName)
-				case "32":
-					depsStruct.Multilib.Lib32.Deps = append(depsStruct.Multilib.Lib32.Deps, fullyQualifiedDepName)
-				case "64", "darwin_universal":
-					depsStruct.Multilib.Lib64.Deps = append(depsStruct.Multilib.Lib64.Deps, fullyQualifiedDepName)
-				case "prefer32", "first_prefer32":
-					depsStruct.Multilib.Prefer32.Deps = append(depsStruct.Multilib.Prefer32.Deps, fullyQualifiedDepName)
-				default:
-					depsStruct.Multilib.Both.Deps = append(depsStruct.Multilib.Both.Deps, fullyQualifiedDepName)
-				}
-			} else if android.InList("64", bitness) {
-				// If only 64 bit variant is enabled
-				depsStruct.Multilib.Lib64.Deps = append(depsStruct.Multilib.Lib64.Deps, fullyQualifiedDepName)
-			} else if android.InList("32", bitness) {
-				// If only 32 bit variant is enabled
-				depsStruct.Multilib.Lib32.Deps = append(depsStruct.Multilib.Lib32.Deps, fullyQualifiedDepName)
-			} else {
-				// If only common variant is enabled
-				depsStruct.Multilib.Common.Deps = append(depsStruct.Multilib.Common.Deps, fullyQualifiedDepName)
-			}
-		}
-		if err := proptools.AppendMatchingProperties(m.GetProperties(), &depsStruct, nil); err != nil {
+		depsStruct := generateDepStruct(*fsDeps[partition])
+		if err := proptools.AppendMatchingProperties(m.GetProperties(), depsStruct, nil); err != nil {
 			mctx.ModuleErrorf(err.Error())
 		}
 	}
 }
 
+func generateDepStruct(deps map[string]*depCandidateProps) *packagingPropsStruct {
+	depsStruct := packagingPropsStruct{}
+	for depName, depProps := range deps {
+		bitness := getBitness(depProps.Arch)
+		fullyQualifiedDepName := fullyQualifiedModuleName(depName, depProps.Namespace)
+		if android.InList("32", bitness) && android.InList("64", bitness) {
+			// If both 32 and 64 bit variants are enabled for this module
+			switch depProps.Multilib {
+			case string(android.MultilibBoth):
+				depsStruct.Multilib.Both.Deps = append(depsStruct.Multilib.Both.Deps, fullyQualifiedDepName)
+			case string(android.MultilibCommon), string(android.MultilibFirst):
+				depsStruct.Deps = append(depsStruct.Deps, fullyQualifiedDepName)
+			case "32":
+				depsStruct.Multilib.Lib32.Deps = append(depsStruct.Multilib.Lib32.Deps, fullyQualifiedDepName)
+			case "64", "darwin_universal":
+				depsStruct.Multilib.Lib64.Deps = append(depsStruct.Multilib.Lib64.Deps, fullyQualifiedDepName)
+			case "prefer32", "first_prefer32":
+				depsStruct.Multilib.Prefer32.Deps = append(depsStruct.Multilib.Prefer32.Deps, fullyQualifiedDepName)
+			default:
+				depsStruct.Multilib.Both.Deps = append(depsStruct.Multilib.Both.Deps, fullyQualifiedDepName)
+			}
+		} else if android.InList("64", bitness) {
+			// If only 64 bit variant is enabled
+			depsStruct.Multilib.Lib64.Deps = append(depsStruct.Multilib.Lib64.Deps, fullyQualifiedDepName)
+		} else if android.InList("32", bitness) {
+			// If only 32 bit variant is enabled
+			depsStruct.Multilib.Lib32.Deps = append(depsStruct.Multilib.Lib32.Deps, fullyQualifiedDepName)
+		} else {
+			// If only common variant is enabled
+			depsStruct.Multilib.Common.Deps = append(depsStruct.Multilib.Common.Deps, fullyQualifiedDepName)
+		}
+	}
+	return &depsStruct
+}
+
 type filesystemCreatorProps struct {
 	Generated_partition_types   []string `blueprint:"mutated"`
 	Unsupported_partition_types []string `blueprint:"mutated"`
@@ -331,10 +345,18 @@
 	ctx.CreateModule(filesystem.AndroidDeviceFactory, baseProps, partitionProps)
 }
 
-var (
-	// https://source.corp.google.com/h/googleplex-android/platform/build/+/639d79f5012a6542ab1f733b0697db45761ab0f3:core/packaging/flags.mk;l=21;drc=5ba8a8b77507f93aa48cc61c5ba3f31a4d0cbf37;bpv=1;bpt=0
-	partitionsWithAconfig = []string{"system", "product", "vendor"}
-)
+func partitionSpecificFsProps(fsProps *filesystem.FilesystemProperties, partitionType string) {
+	switch partitionType {
+	case "system":
+		fsProps.Build_logtags = proptools.BoolPtr(true)
+		// https://source.corp.google.com/h/googleplex-android/platform/build//639d79f5012a6542ab1f733b0697db45761ab0f3:core/packaging/flags.mk;l=21;drc=5ba8a8b77507f93aa48cc61c5ba3f31a4d0cbf37;bpv=1;bpt=0
+		fsProps.Gen_aconfig_flags_pb = proptools.BoolPtr(true)
+	case "product":
+		fsProps.Gen_aconfig_flags_pb = proptools.BoolPtr(true)
+	case "vendor":
+		fsProps.Gen_aconfig_flags_pb = proptools.BoolPtr(true)
+	}
+}
 
 // Creates a soong module to build the given partition. Returns false if we can't support building
 // it.
@@ -406,8 +428,6 @@
 
 	fsProps.Base_dir = proptools.StringPtr(partitionType)
 
-	fsProps.Gen_aconfig_flags_pb = proptools.BoolPtr(android.InList(partitionType, partitionsWithAconfig))
-
 	fsProps.Is_auto_generated = proptools.BoolPtr(true)
 
 	// Identical to that of the generic_system_image
@@ -420,6 +440,9 @@
 		"framework/*/*",     // framework/{arch}
 		"framework/oat/*/*", // framework/oat/{arch}
 	}
+	fsProps.Fsverity.Libs = []string{":framework-res{.export-package.apk}"}
+
+	partitionSpecificFsProps(fsProps, partitionType)
 
 	// system_image properties that are not set:
 	// - filesystemProperties.Avb_hash_algorithm
@@ -431,7 +454,6 @@
 	// - filesystemProperties.Mount_point
 	// - filesystemProperties.Include_make_built_files
 	// - filesystemProperties.Build_logtags
-	// - filesystemProperties.Fsverity.Libs
 	// - systemImageProperties.Linker_config_src
 
 	return fsProps, true
@@ -499,10 +521,14 @@
 
 	var diffTestFiles []android.Path
 	for _, partitionType := range f.properties.Generated_partition_types {
-		diffTestFiles = append(diffTestFiles, f.createDiffTest(ctx, partitionType))
+		diffTestFile := f.createDiffTest(ctx, partitionType)
+		diffTestFiles = append(diffTestFiles, diffTestFile)
+		ctx.Phony(fmt.Sprintf("soong_generated_%s_filesystem_test", partitionType), diffTestFile)
 	}
 	for _, partitionType := range f.properties.Unsupported_partition_types {
-		diffTestFiles = append(diffTestFiles, createFailingCommand(ctx, fmt.Sprintf("Couldn't build %s partition", partitionType)))
+		diffTestFile := createFailingCommand(ctx, fmt.Sprintf("Couldn't build %s partition", partitionType))
+		diffTestFiles = append(diffTestFiles, diffTestFile)
+		ctx.Phony(fmt.Sprintf("soong_generated_%s_filesystem_test", partitionType), diffTestFile)
 	}
 	ctx.Phony("soong_generated_filesystem_tests", diffTestFiles...)
 }
@@ -512,14 +538,14 @@
 	if partitionType != "system" {
 		return ""
 	}
+	fsProps, fsTypeSupported := generateFsProps(ctx, partitionType)
+	if !fsTypeSupported {
+		return ""
+	}
 
 	baseProps := generateBaseProps(proptools.StringPtr(generatedModuleNameForPartition(ctx.Config(), partitionType)))
-	fsProps, _ := generateFsProps(ctx, partitionType)
-
-	deps := ctx.Config().Get(fsGenStateOnceKey).(*FsGenState).fsDeps
-	depProps := &android.PackagingProperties{
-		Deps: android.NewSimpleConfigurable(fullyQualifiedModuleNames(deps[partitionType])),
-	}
+	deps := ctx.Config().Get(fsGenStateOnceKey).(*FsGenState).fsDeps[partitionType]
+	depProps := generateDepStruct(*deps)
 
 	result, err := proptools.RepackProperties([]interface{}{baseProps, fsProps, depProps})
 	if err != nil {
diff --git a/java/app.go b/java/app.go
index e112e93..69fdc47 100644
--- a/java/app.go
+++ b/java/app.go
@@ -678,7 +678,7 @@
 		a.dexProperties.Uncompress_dex = proptools.BoolPtr(a.shouldUncompressDex(ctx))
 	}
 	a.dexpreopter.uncompressedDex = *a.dexProperties.Uncompress_dex
-	a.dexpreopter.enforceUsesLibs = a.usesLibrary.enforceUsesLibraries()
+	a.dexpreopter.enforceUsesLibs = a.usesLibrary.enforceUsesLibraries(ctx)
 	a.dexpreopter.classLoaderContexts = a.classLoaderContexts
 	a.dexpreopter.manifestFile = a.mergedManifestFile
 	a.dexpreopter.preventInstall = a.appProperties.PreventInstall
@@ -907,10 +907,10 @@
 	// Process all building blocks, from AAPT to certificates.
 	a.aaptBuildActions(ctx)
 	// The decision to enforce <uses-library> checks is made before adding implicit SDK libraries.
-	a.usesLibrary.freezeEnforceUsesLibraries()
+	a.usesLibrary.freezeEnforceUsesLibraries(ctx)
 
 	// Check that the <uses-library> list is coherent with the manifest.
-	if a.usesLibrary.enforceUsesLibraries() {
+	if a.usesLibrary.enforceUsesLibraries(ctx) {
 		manifestCheckFile := a.usesLibrary.verifyUsesLibrariesManifest(
 			ctx, a.mergedManifestFile, &a.classLoaderContexts)
 		apkDeps = append(apkDeps, manifestCheckFile)
@@ -1686,11 +1686,11 @@
 
 type UsesLibraryProperties struct {
 	// A list of shared library modules that will be listed in uses-library tags in the AndroidManifest.xml file.
-	Uses_libs []string
+	Uses_libs proptools.Configurable[[]string]
 
 	// A list of shared library modules that will be listed in uses-library tags in the AndroidManifest.xml file with
 	// required=false.
-	Optional_uses_libs []string
+	Optional_uses_libs proptools.Configurable[[]string]
 
 	// If true, the list of uses_libs and optional_uses_libs modules must match the AndroidManifest.xml file.  Defaults
 	// to true if either uses_libs or optional_uses_libs is set.  Will unconditionally default to true in the future.
@@ -1738,7 +1738,7 @@
 
 func (u *usesLibrary) deps(ctx android.BottomUpMutatorContext, addCompatDeps bool) {
 	if !ctx.Config().UnbundledBuild() || ctx.Config().UnbundledBuildImage() {
-		ctx.AddVariationDependencies(nil, usesLibReqTag, u.usesLibraryProperties.Uses_libs...)
+		ctx.AddVariationDependencies(nil, usesLibReqTag, u.usesLibraryProperties.Uses_libs.GetOrDefault(ctx, nil)...)
 		presentOptionalUsesLibs := u.presentOptionalUsesLibs(ctx)
 		ctx.AddVariationDependencies(nil, usesLibOptTag, presentOptionalUsesLibs...)
 		// Only add these extra dependencies if the module is an app that depends on framework
@@ -1751,17 +1751,17 @@
 			ctx.AddVariationDependencies(nil, usesLibCompat28OptTag, dexpreopt.OptionalCompatUsesLibs28...)
 			ctx.AddVariationDependencies(nil, usesLibCompat30OptTag, dexpreopt.OptionalCompatUsesLibs30...)
 		}
-		_, diff, _ := android.ListSetDifference(u.usesLibraryProperties.Optional_uses_libs, presentOptionalUsesLibs)
+		_, diff, _ := android.ListSetDifference(u.usesLibraryProperties.Optional_uses_libs.GetOrDefault(ctx, nil), presentOptionalUsesLibs)
 		u.usesLibraryProperties.Missing_optional_uses_libs = diff
 	} else {
-		ctx.AddVariationDependencies(nil, r8LibraryJarTag, u.usesLibraryProperties.Uses_libs...)
+		ctx.AddVariationDependencies(nil, r8LibraryJarTag, u.usesLibraryProperties.Uses_libs.GetOrDefault(ctx, nil)...)
 		ctx.AddVariationDependencies(nil, r8LibraryJarTag, u.presentOptionalUsesLibs(ctx)...)
 	}
 }
 
 // presentOptionalUsesLibs returns optional_uses_libs after filtering out libraries that don't exist in the source tree.
 func (u *usesLibrary) presentOptionalUsesLibs(ctx android.BaseModuleContext) []string {
-	optionalUsesLibs := android.FilterListPred(u.usesLibraryProperties.Optional_uses_libs, func(s string) bool {
+	optionalUsesLibs := android.FilterListPred(u.usesLibraryProperties.Optional_uses_libs.GetOrDefault(ctx, nil), func(s string) bool {
 		exists := ctx.OtherModuleExists(s)
 		if !exists && !android.InList(ctx.ModuleName(), ctx.Config().BuildWarningBadOptionalUsesLibsAllowlist()) {
 			fmt.Printf("Warning: Module '%s' depends on non-existing optional_uses_libs '%s'\n", ctx.ModuleName(), s)
@@ -1827,15 +1827,15 @@
 // enforceUsesLibraries returns true of <uses-library> tags should be checked against uses_libs and optional_uses_libs
 // properties.  Defaults to true if either of uses_libs or optional_uses_libs is specified.  Will default to true
 // unconditionally in the future.
-func (u *usesLibrary) enforceUsesLibraries() bool {
-	defaultEnforceUsesLibs := len(u.usesLibraryProperties.Uses_libs) > 0 ||
-		len(u.usesLibraryProperties.Optional_uses_libs) > 0
+func (u *usesLibrary) enforceUsesLibraries(ctx android.ModuleContext) bool {
+	defaultEnforceUsesLibs := len(u.usesLibraryProperties.Uses_libs.GetOrDefault(ctx, nil)) > 0 ||
+		len(u.usesLibraryProperties.Optional_uses_libs.GetOrDefault(ctx, nil)) > 0
 	return BoolDefault(u.usesLibraryProperties.Enforce_uses_libs, u.enforce || defaultEnforceUsesLibs)
 }
 
 // Freeze the value of `enforce_uses_libs` based on the current values of `uses_libs` and `optional_uses_libs`.
-func (u *usesLibrary) freezeEnforceUsesLibraries() {
-	enforce := u.enforceUsesLibraries()
+func (u *usesLibrary) freezeEnforceUsesLibraries(ctx android.ModuleContext) {
+	enforce := u.enforceUsesLibraries(ctx)
 	u.usesLibraryProperties.Enforce_uses_libs = &enforce
 }
 
diff --git a/java/app_import.go b/java/app_import.go
index f5d9f3e..6b88f1c 100644
--- a/java/app_import.go
+++ b/java/app_import.go
@@ -364,13 +364,13 @@
 	a.dexpreopter.isPresignedPrebuilt = Bool(a.properties.Presigned)
 	a.dexpreopter.uncompressedDex = a.shouldUncompressDex(ctx)
 
-	a.dexpreopter.enforceUsesLibs = a.usesLibrary.enforceUsesLibraries()
+	a.dexpreopter.enforceUsesLibs = a.usesLibrary.enforceUsesLibraries(ctx)
 	a.dexpreopter.classLoaderContexts = a.usesLibrary.classLoaderContextForUsesLibDeps(ctx)
 	if a.usesLibrary.shouldDisableDexpreopt {
 		a.dexpreopter.disableDexpreopt()
 	}
 
-	if a.usesLibrary.enforceUsesLibraries() {
+	if a.usesLibrary.enforceUsesLibraries(ctx) {
 		a.usesLibrary.verifyUsesLibrariesAPK(ctx, srcApk, &a.dexpreopter.classLoaderContexts)
 	}
 
diff --git a/java/base.go b/java/base.go
index a9399cb..f075dbd 100644
--- a/java/base.go
+++ b/java/base.go
@@ -113,6 +113,9 @@
 	// List of modules to use as annotation processors
 	Plugins []string
 
+	// List of modules to use as kotlin plugin
+	Kotlin_plugins []string
+
 	// List of modules to export to libraries that directly depend on this library as annotation
 	// processors.  Note that if the plugins set generates_api: true this will disable the turbine
 	// optimization on modules that depend on this module, which will reduce parallelism and cause
@@ -862,7 +865,7 @@
 					// explicitly listed in the optional_uses_libs property.
 					tag := usesLibReqTag
 					if android.InList(*lib, dexpreopt.OptionalCompatUsesLibs) ||
-						android.InList(*lib, j.usesLibrary.usesLibraryProperties.Optional_uses_libs) {
+						android.InList(*lib, j.usesLibrary.usesLibraryProperties.Optional_uses_libs.GetOrDefault(ctx, nil)) {
 						tag = usesLibOptTag
 					}
 					ctx.AddVariationDependencies(nil, tag, *lib)
@@ -872,6 +875,7 @@
 	}
 
 	ctx.AddFarVariationDependencies(ctx.Config().BuildOSCommonTarget.Variations(), pluginTag, j.properties.Plugins...)
+	ctx.AddFarVariationDependencies(ctx.Config().BuildOSCommonTarget.Variations(), kotlinPluginTag, j.properties.Kotlin_plugins...)
 	ctx.AddFarVariationDependencies(ctx.Config().BuildOSCommonTarget.Variations(), errorpronePluginTag, j.properties.Errorprone.Extra_check_modules...)
 	ctx.AddFarVariationDependencies(ctx.Config().BuildOSCommonTarget.Variations(), exportedPluginTag, j.properties.Exported_plugins...)
 
@@ -904,7 +908,7 @@
 
 	if j.useCompose(ctx) {
 		ctx.AddVariationDependencies(ctx.Config().BuildOSCommonTarget.Variations(), kotlinPluginTag,
-			"androidx.compose.compiler_compiler-hosted")
+			"androidx.compose.compiler_compiler-hosted-plugin")
 	}
 }
 
@@ -2499,7 +2503,11 @@
 					ctx.PropertyErrorf("exported_plugins", "%q is not a java_plugin module", otherName)
 				}
 			case kotlinPluginTag:
-				deps.kotlinPlugins = append(deps.kotlinPlugins, dep.ImplementationAndResourcesJars...)
+				if _, ok := module.(*KotlinPlugin); ok {
+					deps.kotlinPlugins = append(deps.kotlinPlugins, dep.ImplementationAndResourcesJars...)
+				} else {
+					ctx.PropertyErrorf("kotlin_plugins", "%q is not a kotlin_plugin module", otherName)
+				}
 			case syspropPublicStubDepTag:
 				// This is a sysprop implementation library, forward the JavaInfoProvider from
 				// the corresponding sysprop public stub library as SyspropPublicStubInfoProvider.
diff --git a/java/java.go b/java/java.go
index 288042b..8b30262 100644
--- a/java/java.go
+++ b/java/java.go
@@ -3343,7 +3343,7 @@
 	if sdkLib != nil {
 		optional := false
 		if module, ok := ctx.Module().(ModuleWithUsesLibrary); ok {
-			if android.InList(*sdkLib, module.UsesLibrary().usesLibraryProperties.Optional_uses_libs) {
+			if android.InList(*sdkLib, module.UsesLibrary().usesLibraryProperties.Optional_uses_libs.GetOrDefault(ctx, nil)) {
 				optional = true
 			}
 		}
diff --git a/java/kotlin_test.go b/java/kotlin_test.go
index f6e7fca..45eac01 100644
--- a/java/kotlin_test.go
+++ b/java/kotlin_test.go
@@ -500,8 +500,8 @@
 			name: "androidx.compose.runtime_runtime",
 		}
 
-		java_library_host {
-			name: "androidx.compose.compiler_compiler-hosted",
+		kotlin_plugin {
+			name: "androidx.compose.compiler_compiler-hosted-plugin",
 		}
 
 		java_library {
@@ -523,7 +523,7 @@
 
 	buildOS := result.Config.BuildOS.String()
 
-	composeCompiler := result.ModuleForTests("androidx.compose.compiler_compiler-hosted", buildOS+"_common").Rule("combineJar").Output
+	composeCompiler := result.ModuleForTests("androidx.compose.compiler_compiler-hosted-plugin", buildOS+"_common").Rule("combineJar").Output
 	withCompose := result.ModuleForTests("withcompose", "android_common")
 	noCompose := result.ModuleForTests("nocompose", "android_common")
 
@@ -542,3 +542,50 @@
 	android.AssertStringDoesNotContain(t, "unexpected compose compiler plugin",
 		noCompose.VariablesForTestsRelativeToTop()["kotlincFlags"], "-Xplugin="+composeCompiler.String())
 }
+
+func TestKotlinPlugin(t *testing.T) {
+	result := android.GroupFixturePreparers(
+		PrepareForTestWithJavaDefaultModules,
+	).RunTestWithBp(t, `
+		kotlin_plugin {
+			name: "kotlin_plugin",
+		}
+
+		java_library {
+			name: "with_kotlin_plugin",
+			srcs: ["a.kt"],
+			plugins: ["plugin"],
+			kotlin_plugins: ["kotlin_plugin"],
+		}
+
+		java_library {
+			name: "no_kotlin_plugin",
+			srcs: ["a.kt"],
+		}
+
+		java_plugin {
+			name: "plugin",
+		}
+	`)
+
+	buildOS := result.Config.BuildOS.String()
+
+	kotlinPlugin := result.ModuleForTests("kotlin_plugin", buildOS+"_common").Rule("combineJar").Output
+	withKotlinPlugin := result.ModuleForTests("with_kotlin_plugin", "android_common")
+	noKotlinPlugin := result.ModuleForTests("no_kotlin_plugin", "android_common")
+
+	android.AssertStringListContains(t, "missing plugin compiler dependency",
+		withKotlinPlugin.Rule("kotlinc").Implicits.Strings(), kotlinPlugin.String())
+
+	android.AssertStringDoesContain(t, "missing kotlin plugin",
+		withKotlinPlugin.VariablesForTestsRelativeToTop()["kotlincFlags"], "-Xplugin="+kotlinPlugin.String())
+
+	android.AssertStringListContains(t, "missing kapt kotlin plugin dependency",
+		withKotlinPlugin.Rule("kapt").Implicits.Strings(), kotlinPlugin.String())
+
+	android.AssertStringListDoesNotContain(t, "unexpected kotlin plugin dependency",
+		noKotlinPlugin.Rule("kotlinc").Implicits.Strings(), kotlinPlugin.String())
+
+	android.AssertStringDoesNotContain(t, "unexpected kotlin plugin",
+		noKotlinPlugin.VariablesForTestsRelativeToTop()["kotlincFlags"], "-Xplugin="+kotlinPlugin.String())
+}
diff --git a/java/plugin.go b/java/plugin.go
index 9c4774a..610c9fd 100644
--- a/java/plugin.go
+++ b/java/plugin.go
@@ -24,6 +24,7 @@
 
 func registerJavaPluginBuildComponents(ctx android.RegistrationContext) {
 	ctx.RegisterModuleType("java_plugin", PluginFactory)
+	ctx.RegisterModuleType("kotlin_plugin", KotlinPluginFactory)
 }
 
 func PluginFactory() android.Module {
@@ -37,6 +38,16 @@
 	return module
 }
 
+func KotlinPluginFactory() android.Module {
+	module := &KotlinPlugin{}
+
+	module.addHostProperties()
+
+	InitJavaModule(module, android.HostSupported)
+
+	return module
+}
+
 // Plugin describes a java_plugin module, a host java library that will be used by javac as an annotation processor.
 type Plugin struct {
 	Library
@@ -53,3 +64,8 @@
 	// parallelism and cause more recompilation for modules that depend on modules that use this plugin.
 	Generates_api *bool
 }
+
+// Plugin describes a kotlin_plugin module, a host java/kotlin library that will be used by kotlinc as a compiler plugin.
+type KotlinPlugin struct {
+	Library
+}
diff --git a/java/sdk_library_internal.go b/java/sdk_library_internal.go
index ca088cf..768e57a 100644
--- a/java/sdk_library_internal.go
+++ b/java/sdk_library_internal.go
@@ -566,7 +566,7 @@
 		Min_device_sdk            *string
 		Max_device_sdk            *string
 		Sdk_library_min_api_level *string
-		Uses_libs_dependencies    []string
+		Uses_libs_dependencies    proptools.Configurable[[]string]
 	}{
 		Name:                      proptools.StringPtr(module.xmlPermissionsModuleName()),
 		Enabled:                   module.EnabledProperty(),
@@ -577,7 +577,7 @@
 		Min_device_sdk:            module.commonSdkLibraryProperties.Min_device_sdk,
 		Max_device_sdk:            module.commonSdkLibraryProperties.Max_device_sdk,
 		Sdk_library_min_api_level: &moduleMinApiLevelStr,
-		Uses_libs_dependencies:    module.usesLibraryProperties.Uses_libs,
+		Uses_libs_dependencies:    module.usesLibraryProperties.Uses_libs.Clone(),
 	}
 
 	mctx.CreateModule(sdkLibraryXmlFactory, &props)
@@ -742,7 +742,7 @@
 	// Uses-libs dependencies that the shared library requires to work correctly.
 	//
 	// This will add dependency="foo:bar" to the <library> section.
-	Uses_libs_dependencies []string
+	Uses_libs_dependencies proptools.Configurable[[]string]
 }
 
 // java_sdk_library_xml builds the permission xml file for a java_sdk_library.
@@ -864,7 +864,7 @@
 	implicitUntilAttr := formattedOptionalSdkLevelAttribute(ctx, "on-bootclasspath-before", module.properties.On_bootclasspath_before)
 	minSdkAttr := formattedOptionalSdkLevelAttribute(ctx, "min-device-sdk", module.properties.Min_device_sdk)
 	maxSdkAttr := formattedOptionalSdkLevelAttribute(ctx, "max-device-sdk", module.properties.Max_device_sdk)
-	dependenciesAttr := formattedDependenciesAttribute(module.properties.Uses_libs_dependencies)
+	dependenciesAttr := formattedDependenciesAttribute(module.properties.Uses_libs_dependencies.GetOrDefault(ctx, nil))
 	// <library> is understood in all android versions whereas <apex-library> is only understood from API T (and ignored before that).
 	// similarly, min_device_sdk is only understood from T. So if a library is using that, we need to use the apex-library to make sure this library is not loaded before T
 	var libraryTag string
diff --git a/ui/build/config.go b/ui/build/config.go
index 75edfcd..9ec04a0 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -98,7 +98,6 @@
 	buildFromSourceStub      bool
 	incrementalBuildActions  bool
 	ensureAllowlistIntegrity bool // For CI builds - make sure modules are mixed-built
-	partialCompileFlags      partialCompileFlags
 
 	// From the product config
 	katiArgs        []string
@@ -138,16 +137,6 @@
 	ninjaCommand ninjaCommandType
 }
 
-type partialCompileFlags struct {
-	// Is partial compilation enabled at all?
-	enabled bool
-
-	// Whether to use d8 instead of r8
-	use_d8 bool
-
-	// Add others as needed.
-}
-
 type NinjaWeightListSource uint
 
 const (
@@ -304,12 +293,24 @@
 		ret.sandboxConfig.SetSrcDirIsRO(srcDirIsWritable == "false")
 	}
 
-	ret.partialCompileFlags = parsePartialCompileFlags(ctx)
-
 	if os.Getenv("GENERATE_SOONG_DEBUG") == "true" {
 		ret.moduleDebugFile, _ = filepath.Abs(shared.JoinPath(ret.SoongOutDir(), "soong-debug-info.json"))
 	}
 
+	// If SOONG_USE_PARTIAL_COMPILE is set, make it one of "true" or the empty string.
+	// This simplifies the generated Ninja rules, so that they only need to check for the empty string.
+	if value, ok := os.LookupEnv("SOONG_USE_PARTIAL_COMPILE"); ok {
+		if value == "true" || value == "1" || value == "y" || value == "yes" {
+			value = "true"
+		} else {
+			value = ""
+		}
+		err = os.Setenv("SOONG_USE_PARTIAL_COMPILE", value)
+		if err != nil {
+			ctx.Fatalln("Failed to set SOONG_USE_PARTIAL_COMPILE: %v", err)
+		}
+	}
+
 	ret.ninjaCommand = NINJA_NINJA
 	switch os.Getenv("SOONG_NINJA") {
 	case "n2":
@@ -382,7 +383,6 @@
 		// Use config.ninjaCommand instead.
 		"SOONG_NINJA",
 		"SOONG_USE_N2",
-		"SOONG_PARTIAL_COMPILE",
 	)
 
 	if ret.UseGoma() || ret.ForceUseGoma() {
@@ -501,78 +501,6 @@
 	return c
 }
 
-// Parse SOONG_PARTIAL_COMPILE.
-//
-// The user-facing documentation shows:
-//
-// - empty or not set: "The current default state"
-// - "true" or "on": enable all stable partial compile features.
-// - "false" or "off": disable partial compile completely.
-//
-// What we actually allow is a comma separated list of tokens, whose first
-// character may be "+" (enable) or "-" (disable).  If neither is present, "+"
-// is assumed.  For example, "on,+use_d8" will enable partial compilation, and
-// additionally set the use_d8 flag (regardless of whether it is opt-in or
-// opt-out).
-//
-// To add a new feature to the list, add the field in the struct
-// `partialCompileFlags` above, and then add the name of the field in the
-// switch statement below.
-func parsePartialCompileFlags(ctx Context) partialCompileFlags {
-	defaultFlags := partialCompileFlags{
-		// Set any opt-out flags here.  Opt-in flags are off by default.
-		enabled: false,
-	}
-	value, ok := os.LookupEnv("SOONG_PARTIAL_COMPILE")
-
-	if !ok {
-		return defaultFlags
-	}
-
-	ret := defaultFlags
-	tokens := strings.Split(strings.ToLower(value), ",")
-	makeVal := func(state string, defaultValue bool) bool {
-		switch state {
-		case "":
-			return defaultValue
-		case "-":
-			return false
-		case "+":
-			return true
-		}
-		return false
-	}
-	for _, tok := range tokens {
-		var state string
-		switch tok[0:1] {
-		case "":
-			// Ignore empty tokens.
-			continue
-		case "-", "+":
-			state = tok[0:1]
-			tok = tok[1:]
-		default:
-			// Treat `feature` as `+feature`.
-			state = "+"
-		}
-		switch tok {
-		case "true", "on", "yes":
-			ret = defaultFlags
-			ret.enabled = true
-		case "false", "off", "no":
-			// Set everything to false.
-			ret = partialCompileFlags{}
-		case "enabled":
-			ret.enabled = makeVal(state, defaultFlags.enabled)
-		case "use_d8":
-			ret.use_d8 = makeVal(state, defaultFlags.use_d8)
-		default:
-			ctx.Fatalln("Unknown SOONG_PARTIAL_COMPILE value:", value)
-		}
-	}
-	return ret
-}
-
 // NewBuildActionConfig returns a build configuration based on the build action. The arguments are
 // processed based on the build action and extracts any arguments that belongs to the build action.
 func NewBuildActionConfig(action BuildAction, dir string, ctx Context, args ...string) Config {
@@ -1855,10 +1783,6 @@
 	return c.ensureAllowlistIntegrity
 }
 
-func (c *configImpl) PartialCompileFlags() partialCompileFlags {
-	return c.partialCompileFlags
-}
-
 // Returns a Time object if one was passed via a command-line flag.
 // Otherwise returns the passed default.
 func (c *configImpl) BuildStartedTimeOrDefault(defaultTime time.Time) time.Time {
diff --git a/ui/build/kati.go b/ui/build/kati.go
index 5743ff7..4dfb710 100644
--- a/ui/build/kati.go
+++ b/ui/build/kati.go
@@ -183,6 +183,23 @@
 		username = usernameFromEnv
 	}
 
+	// SOONG_USE_PARTIAL_COMPILE may be used in makefiles, but both cases must be supported.
+	//
+	// In general, the partial compile features will be implemented in Soong-based rules. We
+	// also allow them to be used in makefiles.  Clear the environment variable when calling
+	// kati so that we avoid reanalysis when the user changes it.  We will pass it to Ninja.
+	// As a result, rules where we want to allow the developer to toggle the feature ("use
+	// the partial compile feature" vs "legacy, aka full compile behavior") need to use this
+	// in the rule, since changing it will not cause reanalysis.
+	//
+	// Shell syntax in the rule might look something like this:
+	//     if [[ -n ${SOONG_USE_PARTIAL_COMPILE} ]]; then
+	//         # partial compile behavior
+	//     else
+	//         # legacy behavior
+	//     fi
+	cmd.Environment.Unset("SOONG_USE_PARTIAL_COMPILE")
+
 	hostname, ok := cmd.Environment.Get("BUILD_HOSTNAME")
 	// Unset BUILD_HOSTNAME during kati run to avoid kati rerun, kati will use BUILD_HOSTNAME from a file.
 	cmd.Environment.Unset("BUILD_HOSTNAME")
diff --git a/ui/build/ninja.go b/ui/build/ninja.go
index def0783..f5f637f 100644
--- a/ui/build/ninja.go
+++ b/ui/build/ninja.go
@@ -241,6 +241,9 @@
 			"SOONG_USE_N2",
 			"RUST_BACKTRACE",
 			"RUST_LOG",
+
+			// SOONG_USE_PARTIAL_COMPILE only determines which half of the rule we execute.
+			"SOONG_USE_PARTIAL_COMPILE",
 		}, config.BuildBrokenNinjaUsesEnvVars()...)...)
 	}